Assays for detecting positively charged molecules can be adversely impacted by adsorption (retention) of those molecules to a negatively charged surface such as those often present during an analytical assay. Such adsorption can substantially decrease sensitivity and reproducibility of the assay, thereby making the assay less accurate and less useful.
Aminoglycosides are one class of positively charged molecules that adsorb to a negatively charged surface. More particularly, the aminoglycosides can be adsorbed to glass vessels (e.g., cuvettes), tubing, and the like which are often components of commercial autoanalyzers. Adsorption of the aminoglycosides to such surfaces will reduce or eliminate presence of the aminoglycoside in a sample, thus interfering with the assay. Analysis of samples comprising trace quantities of certain aminoglycosides is particularly affected by the adsorption.
Accurate detection of positively charged molecules, such as aminoglycosides, is important in several respects. For example, it is often desirable to know how much of a therapeutic aminoglycoside is present in a biological sample, such as a fluid sample obtained from a patient. Specific assays for detecting therapeutic aminoglycosides and other positively charged molecules are known. For example, homogenous enzyme immunoassays such as EMIT.RTM. have been used to detect gentamicin, netilmicin, tobramycin, vancomycin and other therapeutics. See generally Levy, M. J. and A. P. Jaklitsch (1993) Homogenous Enzyme Immunoassays: EMIT.RTM.in Diagnostics in the Year 2000 Antibody, Biosensor, and Nucleic Acid Technologies (Singh, P. et al. Eds.) Van Nostrand Reinhold, New York and references cited therein.
U.S. Pat. No. 4,220,722 ('722 patent) and U.S. Pat. No. 4,328,311 ('311 patent) each disclose certain enzyme conjugates of aminoglycosides and their use in immunoassays.
U.S. Pat. No. 4,816,391 ('391 patent) discloses use of polyamines that are reported to decrease or prevent adsorption of aminoglycosides to glass surfaces. The polyamines are reported to include amino-substituted dextran, polyethylene amine, and large polymeric amines such as polybrene polyethylene polyamine (sometimes referred to as Polybrene.RTM.).
However, use of polyamines to decrease adsorption of positively charged molecules such as aminoglycosides has significant shortcomings. For example, use of large polymeric amines can complicate steps to remove same from many glass surfaces. Further, there is recognition that use of certain large polymeric amines such as Polybrene.RTM. can complicate assays such as immunoassays. In particular, there is recognition that Polybrene.RTM. is difficult to remove from glass cuvettes present in most autoanalyzers. This difficulty has contributed to poor precision and inaccurate results in many instances. More specifically, glass cuvettes that have been exposed to Polybrene.RTM.-containing calibrators behave differently from those which are not exposed. This problem can increase cost and labor associated with performing the analysis.
Accordingly, effective methods for substantially reducing or eliminating adsorption of positively charged molecules to negatively charged surfaces are desired. Particularly desired is effective methods for substantially reducing adsorption of aminoglycosides to the negatively charged surfaces such as glass and plastic.